Discussion Forum - Northstar Chevelle Club

Grajmahal · Active Member

Posi hunting - 10 bolt for '66. Got something lying around?

OscarZ · Mega Poster

Does Loosie have an overdrive transmission? 4.11 is a pretty low gear ratio for Loosie not racing.

Grajmahal · Active Member

Good question, Michael. In fact, that is the reason for the switch - Loosie is getting a Tremec to replace her Muncie. With a .50:1 OD, she should be all kinds of fun in town and still reasonable on the road. With the current rear, those OD gears will be way too tall and I'd be going down the highway at idle.

I am open to feedback and suggestions, though, in particular from anyone who has done this conversion. I'd like to get it right the first time.

John

Chris S · Active Member

Are you thinking 5 or 6 speed?

Do you have to cut the floor on that year?

Grajmahal · Active Member

6 speed, and you do have to cut the floor, but it is mostly ahead of the shifter, so the console still fits. The 6 speed starts out about 2.9:1 and winds up at .50:1, which is a giant range. I don't think I would go through the hassle for a 5 speed, but the 6 is just too cool to pass up. Know anyone looking for a newly- rebuilt numbers-correct Muncie for a '66?

Jb

Lost in the 60s · President

Grajmahal wrote:
6 speed, and you do have to cut the floor, but it is mostly ahead of the shifter, so the console still fits. The 6 speed starts out about 2.9:1 and winds up at .50:1, which is a giant range. I don't think I would go through the hassle for a 5 speed, but the 6 is just too cool to pass up. Know anyone looking for a newly- rebuilt numbers-correct Muncie for a '66?

Jb

The "newly rebuilt-numbers correct" part usually means a bigger price tag than available funds, but I'll nibble. Is it an M20 or 21 and what are you going to get for it ?

I have a 4.56 12 bolt posi we could possibly work in on trade. Chris P can change the gears to 4.11. With the 6 speed, you're gonna punish it more than you think...

How much research have you done on this tunnel conversion and the console ? From my experience with a '72, it will take considerable modification of the tunnel and the console may not sit right.

Grajmahal · Active Member

I'm sure we can work something out. I'll grab the numbers off it this afternoon and post them here. It has a rebuilt Hurst competition plus shifter for Chevelle, but the linkages are welded to length and I would recommend swapping out to something adjustable (the 2-3 gate sticks on occasion) . I also have a hurst bench seat lever and white ball that go with it, as well as the bell housing/clutch/flywheel/z-bar. Oh, and it has the beefed-up front bearing. Two summers since the rebuild, so call it 3000 miles.

As for the tunnel butchery, the folks at Hurst posted a play-by-play if this install in a '67, and it appears that most of the mods are ahead of the shifter towards the firewall. They claim that the console will fit - I am skeptical, but they also claim that the carpet will fit.

I would think that 4.56 gears would make first gear more like a rock climber than a street car, but I don't know that for sure. What I have read is that 4.11 is very streetable with this trans, with good manners on the highway as well. I figure that is essentially a 2.05:1 rear on the highway in 6th, which means something on the order of 1600 rpm at cruise speed. You're probably right about the rear getting a little more abuse :)

John

Lost in the 60s · President

The case numbers aren't going to indicate anything, as the 20 and 21 used the same case and side cover. If the input shaft was replaced during the rebuild, that may not indicate anything either. At this point, pulling the side case and counting the teeth on the first gears will be the most accurate way to know what it is. Probably want to wait until it is out for that.

Are you going to a hydraulic clutch release ? If not, you'll most likely want the Z-bar.

Yeah, if you were to leave the 4.56 gears in the rear, you could probably skip using 1st gear in the trans.

Grajmahal · Active Member

Yeah, I'm swapping out for a hydraulic clutch system. Left leg is getting too old :)

Casting numbers: 3851325, with P0204 stamped on the side of the case. From what I can tell, that means that it was produced on February 04, 1965. I don't recall a groove in the input shaft, although my memory is far from infallible. I am guessing that it is an M20 based only on that fact. When I bought it, I was not particularly concerned whether it was a 20 or a 21, I just didn't want an M22 for the noise factor. It shifts crisply and doesn't make any noise except for while sitting in neutral with the clutch out. I assume that this is just countershaft noise, and it isn't a grind or anything, just a subtle whirring. I also never had anything but a single rubber boot between me and the trans, so I have been especially sensitive to any sounds.

If I recall correctly, the tail casing also has an ear or corner that has been welded back on. It doesn't effect the operation of the transmission, but you wouldn't want to have it in a show car where someone might notice the defect (gasp!)

In any event, I will no longer be needing it after the swap, and would be happy to make some kind of a trade. I'm confident in my skills to do the trans swap, but I really do not care to learn how to set up a gear set in a rearend. Some things are best left to experts.

John

Grajmahal · Active Member

While you can't always believe what you read on the internet, Hurst has a pretty good writeup of an installtion into a '67 that makes it look like the tunnel issue isn't a terribly big deal aesthetically : www.hurst-drivelines.com/1967-chevelle-tremec-overdrive-transmission-kit-installation-write-up/

John

Lost in the 60s · President

That trans is a '65 and has the small main shaft. They went to a larger shaft in '66 and up. Not really what I'm looking for but we can talk. I have a small block I could put it behind but they weren't good for a lot of torque from a BB.

Chris P in the club is the rear gear expert for ratio changes.

-- Edited by Lost in the 60s on Friday 13th of May 2016 01:11:07 PM

67ss · 1K+ Club

I am willing to help you guys out but it is going to have to be a new set of gears if you work something out. I have decided it is not worth messing with used gears anymore. Takes way to much time to try and get a good pattern and sometimes you just can't and have to go new anyways.

Grajmahal · Active Member

Chris, I'm fine going with a new gear set, especially if I know it isn't going to be a whiner. Mitch, I thought I had a home run for second there, and I'm down to a base hit. Make me some kind of a trade offer with that 12-bolt if you think you have a use for the Muncie and associated parts. I expect to be doing the swap sometime in June.

John

Lost in the 60s · President

Grajmahal wrote:
While you can't always believe what you read on the internet, Hurst has a pretty good writeup of an installtion into a '67 that makes it look like the tunnel issue isn't a terribly big deal aesthetically : www.hurst-drivelines.com/1967-chevelle-tremec-overdrive-transmission-kit-installation-write-up/

John

That article is for a 5 speed. Is the case the same or larger on the 6 speed ?

Grajmahal · Active Member

So it is. The photos that he sent me of the 6 speed installed are below. The sales rep (and they NEVER lie) tells me that the shifter pops out in exactly the right place for the console, and that the console will sit on the hump with little or no modification. Looking at the photos, that appears to be at least possible as most of that console is behind the shifter. I guess I'm going to find out. I have a repro console, so if there is a little grinding to do here or there it isn't the end of the world.

John

Chris S · Active Member

Does Hurst supply the sheet metal patch for the floor?

I spoke with Silver Sport Transmission and they call it the Perfect Fit Kit. Comes with the tunnel patch and everything else needed to complete the job.

Bobs_Place · Vice President

The pictures look like a 5 speed.

I talked to American Power Train when I was at SEMA, they said they could modify the case on a 5 speed to fit the tunnel with no mods, the 6 speed they said you`d be modifying

The Tremec rep at another booth said the 6 seed was wider in the upper part on the trans and if the shape of the tunnel more squared of up high it might fit with out mods.

Grajmahal · Active Member

Hurst provides the tin and a template, but they do tell you that you have to cut and add material. Not such a big deal as I just did the floor pans, I don't really mind the cut and patch program as long as the fit is guaranteed. Everyone's complaint about this project is the tunnel mods, which seem to me like the easiest part of the job. I'd much rather cut and weld tin than crawl around on a cold concrete floor with a 150 pound transmission on my chest.

Those could be pics of a 5-speed, I don't know - they're the ones that the rep sent to gaue the amount of chop-and-weld that needs to happen to make the install work. He assured me that the factory console would fit - like I say, I guess I'm gonna find out. To my eye, at least the passenger side in the shifter area is not going to fit if the mods are like those in the photos.

I looked at the Silver Sport SST kits as well, but the Hurst setup was about the same money for the entire kit plus the hydraulic clutch conversion. The clutch rig is worth $500-$600 bucks by itself, and I guess I trust the Hurst name a little more, so the choice was made.

I'll take some pics and post them here as the project gets going. Thanks for your input everyone!

John

Chris R · 2K+ Club

The guys to talk to about the 6 speed swap would be Scott Parkhurst and even Keith Anderson. They were running a T56 (I believe) before all these companies come out with Tremec kits.